The present invention relates to a method of manufacturing a granular detergent and its object is to provide a granular detergent having an improved mechanical strength and a low hygroscopicity.
It is admittedly possible to manufacture powdery granular detergents having a size of 8 - 100 mesh, a bulk density of 0.1 - 0.35 and a water content of 1 - 20 wt.% by spray drying a slurry of cleaning materials comprising the surfactant, builder, optical bleaching agent, etc., but a powder granular detergent of this type is generally poor in mechanical strength and possesses considerable hygroscopicity, so that the granular detergents in the prior art show a tendency to collapse partially or get wet and massive caking is apt to occur in the course of transportation or storing thereof.
In the case of West German OLS-2053177 a slurry-state detergent composition containing more than 20 wt.% of sodium silicate was granulated by means of extrusion and the like. These granular detergents were possessed of tackiness, and were covered with sodium tripolyphosphate.
However, the thus obtained granular detergents were deficient in water-solubility, and furthermore it was impossible to control the bulk density thereof.